DESCRIPTION (from applicant's abstract): Dr. Champoux proposes the following studies. With respect to plus strand primer formation, it is proposed to study the cleavage specificity of RNAse H at internal sites and the influence of pre-existing nicks on subsequent cleavages. A random mutagenesis approach in MuLV will be used to define the range of sequence features of polypurine tract and its upstream region that are essential for reverse transcription. In the second area of interest, the displacement synthesis, the nature of interaction between the RT and the DNA will be probed by footprinting, photocrosslinking and use of modified DNA structures. The amino acid residues participating in melting the non-template strand during displacement synthesis will be identified by site-directed mutagenesis of the suspected residues. The energetics of the displacement process will be studied by a novel technique that relies on the measurement of positive supercoils generated during displacement synthesis.